In what may be a record setting evacuation order in a U.S. hazardous materials emergency, officials asked nearly 72,000 residents of Bryan, TX, and parts of Brazos County to leave as a fire on July 30 destroyed an agricultural products distribution center containing 557 tons of fertilizer grade ammonium nitrate.

Gary Brooks, sales manager for Knife River Corp., a highway construction company that neighbors the distribution center, said he was ordered to immediately evacuate more than 250 employees.

"We had to clear out the plant, the railroad yard, the offices, the shops - everything," Brooks said. "They told us to get back at least a mile and a quarter."

The first indication of trouble came shortly before noon when a fire engine pulled into the Knife River parking lot, he said.

"They said they were investigating the possibility of a fire next door," Brooks said. "I asked if there was anything I could do and they said no. They only wanted to use our parking lot for staging."

Within 15 minutes, firefighters ordered Knife River evacuated.

"It started out with just a little smoke coming out of the rafters at this wood frame warehouse," Brooks said.

A statewide alert issued by the Texas State Operations Center listed the contents of the warehouse as including 557 tons of ammonium nitrate, 241 tons of potassium chloride, 140 tons of diammonium phosphate, 31 tons of ammonium sulfate, 30 tons of sulfa magnesium and 7.5 tons of zinc and copper zinc.

Reports indicate that about 40 people sought treatment for respiratory problems at local hospitals during the course of the emergency. The Environmental Protection Agency dispatched aircraft from the Dallas-Fort Worth area to take air samples to determine the toxicity of the plume.

At the height of the emergency, authorities ordered 72,000-plus Bryan and rural Brazos County residents within an eight mile radius of the fire to evacuate. Although it was a mandatory evacuation, it was not enforced beyond closing a major highway to keep onlookers away from the scene.

About 800 evacuees arrived at an indoor sports stadium at Texas A&M University being used as a temporary shelter. By evening, most residents were allowed to return to their homes.

The previous U.S. record for an evacuation prompted by a hazardous materials emergency is believed to have been in Apex, NC, in October 2006 when a fire at a hazardous waste transfer station forced the removal of 19,000 residents for two days.

Brooks said he remained concerned about his facility throughout the emergency.

"Less than 100 yards from the fire is where we have 56,000 gallons of diesel fuel stored for our equipment and trucks," Brooks said. "About 15,000 gallons of burner fuel that we use in our asphalt plant was on site as well."